1. Field of Invention
This invention relates to polymer films. More particularly, this invention relates to ultrathin, blended, cellulose nitrate polymer films and their production.
2. Prior Art
The preparation of cellulose nitrate or methacrylate polymer films on a liquid support, such as water, is known. See for example, U.S. Pat. Nos. 2,537,969, 2,537,970, and 2,607,081. Such patents, however, do not discloses the mixing of cellulose nitrate and methacrylate polymers to form blended polymer films.
U.S. Pat. No. 2,689,187 discloses a process for preparing nitrocellulose films. The films allegedly have thicknesses between 200 and 2,000 angstroms. However, the mixing of other polymers, such as methacrylate polymers, to form blended cellulose nitrate films is not disclosed.
In U.S. Pat. No. 2,760,233, a process is disclosed for preparing curved polymer sheets from methacrylic acid ester polymers. However, the addition of cellulose nitrate is not disclosed nor are specific solvent mixtures and ratios suitable for casting ultrathin, pinhole-free, blended, cellulose nitrate films disclosed nor are any film thicknesses provided.
U.S. Pat No. 3,551,244 discloses a process for preparing on a water surface films having a thickness between 0.05 and 5.0 microns (i.e. between 500 and 50,000 angstroms). The patent discloses that some esters, such as ethyl acetate, are suitable casting solvents and states the polymethylmethacrylate and cellulose nitrate films can be prepared. However, the mixing of polymethylmethacrylate and cellulose nitrate is not disclosed nor are specific solvent mixtures and ratios suitable for casting pinhole-free, blended, cellulose nitrate films having thicknesses less than 400 angstroms.
U.S. Pat. No. 3,767,737 discloses a method for producing on a support liquid nonporous alkyl methacrylate polymer membranes having thicknesses between 0.005 and 0.05 mils. Nevertheless, cellulose nitrate is not disclosed as a polymer suitable for combining with alkyl methacrylate polymers to form blended cellulose nitrate films. In addition, specific mixtures of solvents and appropriate solvent ratios for preparing pinhole-free, blended cellulose nitrate films having thicknesses of 400 angstroms or less are not disclosed.
U.S. Pat. Nos. 4,155,793, 4,279,855 and 4,374,891 disclose processes for preparing substantially void-free, ultrathin, permeable polymeric membranes having thicknesses of 500 angstroms or less. Alkyl acrylate polymers are allegedly suitable for use in the disclosed process. However, only films prepared from organopolysiloxane-polycarbonate interpolymers mixed with polyphenylene oxide are disclosed in the examples. Cellulose nitrate films are not disclosed nor are suitable solvent mixtures and ratios for casting blended cellulose nitrate films having thicknesses of 400 angstroms or less described.
In U.S. Pat. No. 3,933,561, a process for preparing polymer membranes is disclosed. Cellulosic polymers are alleged to be suitable for use in the process. However, the blending of nitrocellulose with methacrylate polymers is not disclosed nor are suitable solvent mixtures and ratios for casting blended cellulose nitrate films having thicknesses of 400 angstroms or less.
Other patents, such as U.S. Pat. Nos. 2,631,334 and 4,393,113, also disclose ultrathin polymeric films. However, no blended cellulose nitrate films are disclosed.
In the prior art, the preparation of ultrathin, pinhole-free, blended, cellulose nitrate, free-standing films having thicknesses of less than 400 angstroms generally has not been disclosed. Usually, prior art polymer films with thicknesses of less than 400 angstroms that are cast contain voids or other macroscopic defects.
Therefore, it is an object of this invention to prepare ultrathin, blended cellulose nitrate polymer films.
It is a further object of this invention to prepare pinhole-free, blended, cellulose nitrate polymeric films.
It is also an object of this invention to prepare blended, cellulose nitrate films having thicknesses of 400 angstroms or less.
These and other objects are obtained by the products and process of the present invention.